A cellular communication system is a communication system which controls communications of terminals within a predetermined region (cell) around a base station. In an existing general cellular communication system, signals transmitted from the base station to the terminal are transmitted through a downlink, and signals transmitted from the terminal to the base station are transmitted through an uplink. In the above-mentioned uplink and downlink, a frequency division duplex mode in which division of a frequency domain is made in the same time domain or a time division duplex mode in which division of a time domain is made in the same frequency domain is used.
Up to now, in the cellular communication system, only transmission of signals between the base station and the terminals through the uplink and the downlink has been discussed. However, the case in which communication is directly made between the terminals within the same cell or the base station and the terminals simultaneously transmit or receive signals via a repeater may also be considered.
However, as illustrated in FIG. 1, in the existing cellular communication system, in the case in which communication is made between a first terminal 101 and a second terminal 103 within the same cell (for example, in the case in which the first terminal 101 transmits a signal to the second terminal 103), the signal is transmitted twice via the base station 100, that is, once through the uplink from the first terminal 101 to the base station 100 and once through the downlink from the base station 100 to the second terminal 103. Therefore, double time and frequency bands are required as compared to the case in which communication is directly made between the first and second terminals 101 and 103.